This invention relates generally to dosimetry and workpiece neutralization for ion beam processing of workpieces, and, more particularly to dosimetry and workpiece neutralization for gas cluster ion beam (GCIB) processing.
The use of a GCIB for etching, cleaning, and smoothing of the surfaces of various materials is known in the art (See for example, U.S. Pat. No. 5,814,194, Deguchi, et al., xe2x80x9cSubstrate Surface Treatment Methodxe2x80x9d, 1998). Means for creation of and acceleration of such GCIBs are also described in the Deguchi reference. It is also known (U.S. Pat. No. 5,459,326, Yamada, xe2x80x9cMethod for Surface Treatment with Extra-Low-Speed Ion Beamxe2x80x9d, 1995) that atoms in a cluster ion are not individually energetic enough (on the order of a few electron volts) to significantly penetrate a surface to cause the residual sub-surface damage typically associated with the other types of ion beam processing in which individual ions may have energies on the order of thousands of electron volts. Nevertheless, the cluster ions themselves can be made sufficiently energetic (some thousands of electron volts), to effectively etch, smooth or clean surfaces as shown by Yamada and Matsuo (in xe2x80x9cCluster ion beam processingxe2x80x9d, Matl. Science in Semiconductor Processing I, (1998) pp 27-41).
Since GCIBs contain ionized particles that carry electrical charge, a measure of the processing dose a workpiece receives is the amount of charge (amp-seconds) received by a unit area of the workpiece, measured in amp-seconds per square centimeter, for example. For insulating, partly insulating, or semiconductive workpieces, ion beam processing can induce charging of the workpiece undergoing ion beam processing. An advantage of GCIB processing over some more conventional ion beam processes is that, because of the relatively large mass to charge ratio of the cluster ions compared to conventional atomic or molecular ions, processing can often be effected with less transfer of charge to the workpiece. Nevertheless, workpiece charging is still a concern and means are needed to reduce the degree of such charging during GCIB processing of workpieces.
It is therefore an object of this invention to provide apparatus and methods for measuring and controlling the processing dose received by a workpiece.
It is a further object of this invention to measure and control the amount of charge or surface charging that is or may be received by a workpiece during GCIB processing.
The objects set forth above as well as further and other objects and advantages of the present invention are achieved by the embodiments of the invention described hereinbelow.
A gas cluster ion beam processing apparatus treats a workpiece with a gas cluster ion beam to effect surface modification such as smoothing, etching, cleaning, deposition, etc. A neutralizer is provided to reduce surface charging of the workpiece by the GCIB. A single Faraday cup sensor is used to measure the GCIB current for dosimetry and scanning uniformity control and also to measure and control the degree of surface charging that may be induced in the workpiece during processing.
To insure uniform processing, X-Y mechanical scanning of the workpiece relative to the GCIB is used to distribute the beam effects over the surface or the workpiece. The mechanical scanning mechanism moves the workpiece in an orthogonal raster pattern through the GCIB and also out of the beam at least once each processing cycle. At that time, the GCIB current is measured by an electron suppressed Faraday cup. However, with an improved switching and control technique, the Faraday cup can also be used to measure the total current for workpiece charging and, thus, may control a charge neutralization system or provide a display and an alarm and/or interlock to indicate an undesirable workpiece charging condition. To provide this charging current sensing feature, the suppression voltage on the Faraday cup bias ring is removed. This allows electrons as well as gas cluster ions to be sensed by the Faraday cup. Measurement of the charging can then be accomplished by measuring the net current in the Faraday cup.
For a better understanding of the present invention, together with other and further objects thereof, reference is made to the accompanying drawings and detailed description and its scope will be pointed out in the appended claims.